1. Field of the Invention
The following generally relates to satellite position location systems, and more particularly, to a system, device and method for providing location services using an assisted-Global Navigation Satellite System (“A-GNSS”).
2. Background of the Related Art
A Global Navigation Satellite System (“GNSS”) is a system that uses a constellation or plurality of satellites orbiting the earth along with a number of terrestrial devices, such as a positioning receiver, to determine a position anywhere on the earth. The SPS (Satellite Positioning System) is generally unlimited in its coverage area; provides continuous 24-hour coverage regardless of weather conditions; and is highly accurate. A Global Positioning System (“GPS”), GLONASS and GALILEO are examples of the GNSS. In operation, each of the satellites in the constellation continually emits a radio frequency signal (“satellite signal”) at a predetermined frequency.
To determine its position, the positioning receiver may acquire its position on ground, in air or in space based upon the reception of satellite signals from each of a number of the satellites in view of the positioning receiver (“in-view satellites”). To facilitate such determination, the positioning receiver extracts from each of such satellite signals a time of transmission of such satellite signal (“transmission time”).
Using the transmission time and a time of reception of each of the satellite signals at the positioning receiver (“reception time”), the positioning receiver computes a time delay, which, on a very basic level, is a function of the difference between the transmission and reception times. When computing the delay time, the positioning receiver may also take into account a number of adjustments to (i) normalize differences in time domains between the positioning receiver and the satellite that transmitted the satellite signal, and/or (ii) compensate for atmospheric conditions that affect the transmission time of the satellite signal.
After calculating the time delay, the positioning receiver may multiply the time delay by the speed of light to obtain a distance between the positioning receiver and the satellite that transmitted the satellite signal. By iteratively determining a distance between the positioning receiver and three or more of the remaining in-view satellites, the positioning receiver can determine its position. This process of iteratively determining a distance may be performed by calculating pseudoranges of the satellites.
When the satellite signals are attenuated and/or delayed, however, the positioning receiver cannot calculate the pseudoranges. The satellite signals may be attenuated accurately during their transmission from the satellites to the positioning receiver as a result of buildings, trees, vehicle roof and the like. In some applications of GNSS, such as determining a position (e.g., a location) of a cellular telephone or personal navigation device, when the satellite signals are unacceptably attenuated (“attenuated signals”), then the attenuated signals (i) may not be detected, or (ii) if detected, the attenuated signals cannot be processed or the time required to process is excessive. To improve the processing of the satellite signals the positioning receiver is provided with assistance data.
The assistance data may include time and frequency information, pseudorange estimation information, position estimation information, ephemeris information, and the like. Commonly assigned U.S. Pat. No. 6,453,237 issued Sep. 17, 2002 describes examples of using assistance data for an assisted-GPS (A-GPS) system, and is incorporated herein by reference in its entirety.
Transmission of assistance data to a GNSS receiver is typically performed via a cellular telephone network. The cost of continuously receiving assistance data via a cellular telephone network is very high. Additionally, a cellular telephone transceiver must be coupled to the GNSS receiver to facilitate reception of the assistance data. Such a cellular transceiver results in unwarranted size, complexity and high cost for a GNSS receiver that is to be used for asset tracking only, i.e., without utilization of the cellular transceiver except for assistance data reception.
Thus, there is a need in the art for a simple GNSS tracking device that utilizes assistance data and a method for determining one or more positions of the GNSS-tracking device.